Fluorine-containing vinyl ether compounds, in particular perfluorovinyl ether compounds, are industrially important monomers, because they can give resins that are excellent in physical and chemical properties, such as chemical resistance, heat resistance, low refractive index, and low intermolecular interaction, and also in heat processability, by copolymerization with tetrafluoroethylene.
A known method of synthesizing a perfluorovinyl ether compound is to thermally decompose a perfluoro(2-alkoxypropionic acid) derivative, obtained by reaction of a perfluorocarboxylic acid fluoride (perfluoro acyl fluoride) with hexafluoropropylene oxide (HFPO) (formula 1) (see, for example, U.S. Pat. Nos. 3,291,843, 3,321,532, and 3,351,619).

However, it is difficult to produce the desired perfluoro(2-alkoxypropionic acid) derivative in good yield, because of side reactions, such as oligomerization, in the reaction of a perfluorocarboxylic acid fluoride and HFPO. Known means to overcome the problem include, for example, a method of dechlorinating a perfluorodichloroether obtained in reaction of a perfluoroalkyl hypofluoride with 1,2-dichlorodifluoroethylene (formula 2) (see, for example, European Patent Nos. 201,871 and 269,933); a method of chlorinating, fluorinating, and dechlorinating, in this order, a vinyl ether obtained in reaction of a perfluoroalkyl methoxide with tetrafluoroethylene (formula 3) (see, for example, U.S. Pat. No. 5,350,497, and Journal of Organic Chemistry, Vol. 59 (1994) 4332–4335).

However, it is not feasible industrially to use the method of formula 2, because the reaction of a perfluoroalkyl hypofluoride with 1,2-dichlorodifluoroethylene should be performed at an extremely low temperature. Further, the method of formula 3 has such problems that the reaction proceeds in multiple reaction steps; tetrafluoroethylene used in the reaction is a substance whose transport is prohibited and that should be produced at the same production site; and chlorine gas, which is difficult to handle, should be used. Further, in the methods of formula 1, 2 or 3, there is limitation on the structure of the perfluorovinyl ether possibly produced, because of restriction on the availability of fluorocompounds that are raw materials.
Disclosed as means to overcome these problems are a method of chlorinating, fluorinating, and dechlorinating a desired vinyl ether once prepared (formula 4) (see, for example, Journal of Fluorine Chemistry, 112 (2001) 109–116); and a method of fluorinating and thermally decomposing a desired 2-alkoxypropionic acid derivative once prepared (formulae 5 and 6) (e.g. Journal of Fluorine Chemistry, 112 (2001) 109–116, and International Patent Publication WO 02/20445 pamphlet); and, it became possible to synthesize perfluorovinyl ethers in various structures by these methods.

In the above formulae, X represents a halogen atom.
However, the method of formula 4 has the problem that it is not so easy to synthesize the vinyl ether. That is, a vinyl ether can be prepared, for example, by (1) reaction of an alcohol with acetylene, (2) thermal decomposition of an acetaldehyde dialkyl acetal, or (3) de-hydrohalogenation of a 2-halo-1-alkoxyethane; but, these methods also have problems, for example, that it is necessary to use acetylene, a hazardous explosive substance, in the method (1); a high temperature of 300° C. or higher is needed, and the yield is not always good, in the method (2); and, it is difficult to prepare a 2-halo-1-alkoxyethane in good yield, in the method (3). Further, the method of formula 4 also has problems; for example, that dichloroether after chlorination is unstable, and the fluorination yield is not always high. Further, the methods of formula 5 or 6 have a problem in requiring a multi-step process for preparation of a perhalovinyl ether from the starting material 2-halopropionic acid.
As shown in the following formula 7, JP-T-2003–508374 (“JP-T” means searched and published International patent application) describes a synthetic route for preparing an acyl fluoride having a vic-dichloro structure, for use as a precursor of perfluorovinyl ether, by preparing a 1,2-dichlorovinyl ether in reaction of trichloroethylene with an alcohol under a basic condition, and then fluorinating it. However, the synthetic route is not favorable as an industrial-scale method, because the starting material necessary in the synthetic route: trichloroethylene, is an environmental pollution substance designated as a Class-II specified chemical substance under the Law Concerning Examination and Regulation of Manufacture and Handling of Chemical Substances, and there is danger of explosion under the basic condition.

As described above, although there are currently many known methods of synthesizing perfluorovinyl ethers, they carry problems of their own, and there is a strong demand for development of a method to produce perfluorovinyl ether compounds applicable to synthesis of compounds in a variety of structures easily from readily available environment-friendly raw materials.
On the other hand, perfluoro(ω-vinyloxy-1-alkenes), such as perfluoro(4-vinyloxy-1-butene), are known to give amorphous perfluororesins by cyclization-polymerization by a radical initiator (e.g. Nippon Kagakukaishi JP by the Chemical Society of Japan, 2001, No. 12, 659–667). These perfluororesins, which have the characteristics of conventional tetrafluoroethylene-derived fluoropolymers, i.e. properties, such as high heat resistance, high chemical resistance, low refractive index, and low dielectric constant, as well as solubility in solvents and transparency in a wide wavelength range, including ultraviolet, visible, and near-infrared ranges, are useful as high-performance optical materials for pellicle, optical fiber, antireflective film, and the like.
It is possible to synthesize perfluoro(ω-vinyloxy-1-alkenes) by combined use of fluorine-containing fundamental materials, for example, according to the synthetic route to perfluoro(4-vinyloxy-1-butene) (formula 8) described in JP-A-1-143843 (“JP-A” means unexamined published Japanese patent application), the synthetic route to perfluoro(4-vinyloxy-1-butene) (formula 9) described in JP-A-2-311436, or the synthetic route to perfluoro(4-vinyloxy-1-propene) (formula 10) described in JP-A-54-163507, as shown below. However, these methods also had the problems that the raw materials were expensive, the handling efficiency was poor, and the degree of freedom in designing a target molecule was quite low.

As means to solve the above-mentioned problems, JP-A-2001-240576 and JP-A-2005-68044 disclose the methods of using liquid-phase direct fluorination reactions of formula 11 or formula 12, respectively. It became possible to synthesize perfluoro(ω-vinyloxy-1-alkenes) having desirable skeleton by these methods. However, the method of formula 11 has a greater number of steps and is not an efficient and economical method. On the other hand, the method of formula 12 has drastically simplified steps, but it still demands use of a transport-prohibited substance: tetrafluoroethylene.
In the above formulae 1 to 7 and the following formulae 11 and 12, Rf represents a fluorine-containing alkyl group.
